1. Field of the Invention
The present invention relates to laminates of polyfluorocarbon veneer with elastomers or thermoplastic elastomers, including such products as flexible, durable chemical-resistant hose for use in industrial and other applications. Such hose includes inner tube members displaying good flexibility, excellent heat and chemical resistance and which are characterized by a dual-layer feature. This feature relies on an adhesive elastomeric composition which bonds a thin polyfluorocarbon thermoplastic veneer to a substantially non-polar chemical-resistant organic elastomeric or thermoplastic elastomeric outer layer.
2. Description of the Related Art
Various products use laminates of polyfluorocarbon thermoplastics with elastomers or thermoplastic elastomers, but the bond strength is normally below desirable levels. Other products employing elastomeric or thermoplastic elastomer substrates would benefit from facing the substrate with a thin layer of a polyfluorocarbon thermoplastic for altering frictional properties, providing resistance to chemicals encountered in the application or environment, or the like. The inability to achieve a satisfactory and reliable bond in such laminates continues to be a problem in many applications.
Chemical-resistant hose for use in industrial applications such as tank truck transfer hose commonly includes an elastomeric or thermoplastic tube liner, suitable reinforcement, a helical steel wire or wire braid for vacuum resistance, and a suitable cover to provide flexibility and ease of handling. As the tube liner, highly chemical resistant polyfluorocarbon thermoplastics are optimally employed. Polyfluorocarbon thermoplastics such as polytetrafluoroethylene (PTFE) are highly resistant to high temperature and other chemicals due to the compositions' strong interatomic bonds, wherein fluorine atoms substantially shield the carbon chain backbone. Thus, hose employing PTFE tube liners or the like undergo reduced incidence of degradation and deterioration, and generally enjoy a longer service life compared to hose employing tube liners made of other materials, such as cross-linked polyethylene, ethylene propylene diene terpolymer, or chlorosulfonated polyethylene.
Other common problems affecting chemical-resistant transfer hose are likewise addressed through the use of polyfluorocarbon thermoplastic tube liners. In hose utilizing cross-linked polyethylene, fluoro-elastomers (FKM), ethylene propylene diene terpolymer (EPDM), or chlorosulfonated polyethylene (CSM) as the tube liner material, the transfer of clear liquids and solvents frequently results in unacceptable discoloration of such liquids due to the extraction of oils and resins from liner materials. Polyfluorocarbon thermoplastics such as PTFE and tetrafluoroethylene/hexafluoropropylene copolymer (FEP) are not subject to such extraction. Fluid permeation or seepage through cross-linked polyethylene, FKM, EPDM or CSM inner tubes, and ultimately through outer hose layers is also common. Polyfluorocarbon thermoplastics are known to exhibit very low fluid permeation compared to the above materials.
Hose for use in industrial applications, utilizing tube liners or veneers formed from polyfluorocarbon thermoplastics present processing difficulties as well. For hose having an inner diameter of one inch and greater, veneers are typically extruded in thicknesses of about 0.030 inches and greater. This relatively thick veneer is substantially inflexible, and does not exhibit satisfactory coupling retention to permanent fittings.
While polyfluorocarbon thermoplastics may be extruded into relatively thin veneers, e.g., down to about 0.010 inches (0.254 mm) in thickness, the utilization of such thin veneers necessitates the use of a stabilizing component to impart structural strength to the hose which is otherwise prone to kinking as a result of the poor tensile and hoop strength of the polyfluorocarbon thermoplastic material. One typical method of constructing a chemical-resistant composite hose having a thin polyfluorocarbon thermoplastic veneer comprises bonding the veneer to a braided fabric reinforcement layer by means of an adhesive tape wrapped spirally about the liner. Alternately, a polyfluorocarbon thermoplastic veneer may be encased in a rigid material such as fiberglass or metal. In another form, an outer layer formed from an elastomer or a thermoplastic elastomer may be applied over the polyfluorocarbon thermoplastic veneer. Each of these alternatives is deficient. Encasement in fiberglass or metal is time consuming, and results in an inflexible hose which is unacceptable in many environments. The use of an outer elastomeric or thermoplastic elastomer layer telescoped about a veneer, or the use of fabric reinforcement telescoped about the veneer has proven difficult due to the poor adhesion of the polyfluorocarbon material to other hose components. Moreover, application of braided reinforcement materials involve labor- and time consuming braiding techniques.
The use of a dual-layer inner tube for chemical-resistant hose is nonetheless highly desireable. In single-layer inner tube construction, manufacturing defects, abuse or mishandling may result in hose rupture, seepage or leakage. A double-layer inner tube construction would substantially reduce the risk of leakage or rupture. In the event of such damage to the inner layer, of the inner tube the outer elastomeric layer, selected for its outstanding chemical and heat-resistance, would minimize the threat of catastrophic hose failure.
A flexible, structurally stable, kink-resistant, chemical-resistant transfer hose for use in industrial applications which exhibits good coupling retention to fittings, and which is characterized by a dual-layer inner tube comprising a polyfluorocarbon thermoplastic veneer permanently bonded to an outer layer of a suitable chemical-resistant elastomeric material has not been available in the prior art.
In general, there is a need for laminates of thin layers of polyfluorocarbon thermoplastics with elastomers, including thermoplastic elastomers, which possess sufficient bond strength between the layers to ensure the integrity of the laminate.